实体框架代码优先加载父子项 - 子项始终为空

Question

This is my first code-first project and have never had an issue doing this in db-first, that I can remember. So, I'm either missing something obvious or there's a rule I missed somewhere. I do not want to use lazy loading, and have to think that it's not required to do this, given the many examples using eager loading.

Very simple. Parent record is Listing, child records are Bid entities:

public class Listing {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int ListingID { get; set; }

    [Required]
    [StringLength(140)]
    public string Title { get; set; }

    //...etc.

    public List<Bid> Bids { get; set; }

    public Listing() {
        Bids = new List<Bid>();
    }
}

public class Bid {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int BidID { get; set; }

    [Required]
    public decimal Amount { get; set; }

    //...etc.

    public int ListingID { get; set; }

    [ForeignKey("ListingID")]
    public Listing Listing { get; set; }

    public Bid() {
        Listing = new Listing();
    }
}

I'm using Include to pull the child records:

        using (var db = new MyDbContext()) {
            var listing = db.Listings
                .Where(x => x.Active == true && x.UserID == "abc123")
                .Include(x => x.Bids)
                .FirstOrDefault();
        }

Child collection exists but is always empty (Count = 0) - it's not pulling the records. They're definitely in the tables. I can manually query this and get those bid records, no problem. Basically, I need a listing and all of its bids, similar to this:

select l.*, b.*
from Listing l
inner join Bid b on l.ListingID = b.ListingID
where l.Active = 1
and l.UserID = 'abc123'

What's missing? This article says I'm doing it right:

https://msdn.microsoft.com/en-us/data/jj574232.aspx

Answer 1

Figured it out. I KNEW I had done this type of relationship before. I found an older project where I did the exact same thing. All I had to do was remove the constructor in the Bid class. Apparently it goes awry if you specify both sides of the relationship? I don't know...but now it works and it's pulling the expected records. Frustrating! Seems like they could add some validation to help you from shooting yourself in the foot, so easily. If it's not valid, it'd be nice to know for certain.

Everything the same as the OP, save for this class:

public class Bid {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int BidID { get; set; }

    [Required]
    public decimal Amount { get; set; }

    //...etc.

    public int ListingID { get; set; }

    [ForeignKey("ListingID")]
    public Listing Listing { get; set; }

    //public Bid() {
    //    Listing = new Listing();
    //}
}

Answer 2

尝试删除两个类的构造函数。